power: smb1360: add a property to shutdown smb1360 at device power-off

The fuel gauge in smb1360 is active when device powers off with a
battery connected. The FG sampling increases the standby current by
100uA which is undesired when the device is powered-off.

Add an optional property "qcom,shdn-after-pwroff" to shutdown smb1360
when device is powered off. Doing this prevents a 100uA draw after
power-off and does not impact the SOC accuracy as overall device leakage
is much lower when the device is off.

Change-Id: I1f39c5703ddad0ef9aa25fcb05af84a4ba1c5eab
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>